This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-194736 filed on Jul. 3, 2002.
The present invention relates to an electrically-operated actuator system.
The applicant of the present invention has suggested an electrically-operated actuator system that uses a pulse encoder for controlling a rotation angle of an electric motor in JP-A-2002-354885. In this system, the rotation angle is controlled based on pulse signals corresponding to the rotation angle. A motor control circuit operates according to control signals produced by a motor control circuit and supplies driving current to the motor.
The inventors of the present invention experimentally added a reset circuit to the actuator system to control operations of the motor control circuit. The reset circuit turns off the motor control circuit when the voltage applied to the circuit becomes lower than a predetermined level. When the voltage becomes higher than the predetermined level again, the reset circuit turns on the motor control circuit.
However, the motor continues rotating for a while due to the moment of inertia after the motor control circuit is turned off. In other words, the motor control circuit is unable to control the motor after the voltage becomes lower than the predetermined level and the motor stops with a large overrun. If the overrun is very large, the amount of motor rotation while the motor control circuit is turned off is not determined nor the amount of the overrun.
In a rotation angle determination process, the rotation angle of the motor is determined based on an angle shifted from a reference position (relative rotation angle). If the reference position is not accurately determined, the amount of motor rotation is not accurately determined. The actuator may be mechanically controlled for bringing it back to the reference position.
The actuator may be driven until it hits a stopper before the restart to bring it back to the reference position. However, the actuator requires a durable structure to resist the mechanical strain. This increases size and manufacturing cost of the actuator.
The present invention therefore has an objective to provide an electrically-operated actuator in which an electric motor stops with a small overrun when a motor control circuit is turned off. The present invention has another objective to provide an actuator that does not require frequent origin setting operations.
The actuator of the present invention includes an electric motor, a rotation angle determination means, a motor control means, a reset means, a motor driving means, a motor stopping means, and a motor stopping means driving means. The rotation angle determination means determines a rotation angle of an output shaft of the motor based on pulse signals produced according to a rotation angle of the motor.
The motor control means controls operations of the motor based on the rotation angle determined by the rotation angle determination means. The reset means turns off the motor control means when a voltage applied to the motor control means becomes lower than a predetermined level. When the voltage becomes higher than the predetermined level, the reset means turns on the motor control means.
The motor driving means controls driving current supplied to the motor based on control signals from the motor control means. The motor stopping means electrically stops the motor based on control signals from the motor control means. The motor stopping means driving means drives the motor stopping means when the motor control means is turned off by the reset means.
With this configuration, the motor is stopped by electrical breaking. Therefore, the motor is stopped with a small overrun after the motor control means is turned off, that is, an overrun angle is small. Since the rotation angle at the restart is not much different from the angle at the stop, the angle shifted after the motor control means stops is easily determined. The reference position determination is not required upon the restart of the motor. Therefore, the number of the origin setting operations reduces, in other words, the actuator does not require a durable construction. Thus, size and manufacturing cost of the actuator are reduced.